1. Field of the Invention
The present invention relates to a TV camera, particularly a TV camera with focus detecting means.
2. Description of the Prior Art
Most of the TV camera focus detecting or automatic focus adjusting devices that have been proposed operate by utilizing the time serial image signals generated in the image pick up device and utilizing the picture image signal for one portion corresponding to the measuring view field so as to evaluate the focus of image formed. However, the evaluation of the picture image signal for one portion is not sufficient to determine whether the image is focused in front of the sensing surface or behind it, i.e., whether it is the near-focus state or the far-focus state although the in-focus state can be detected. If the televised object is in motion, the vibration of the camera or the variation of the object brightness during the measurement causes the evaluation signal (hereinafter called focus signal) to fluctuate in such a manner that practical focus adjustment is almost impossible.
In order to avoid this type of inconvenience, a so-called focus modulation method is used. This method involves arranging a vibrating optical device in the optical path. In view of the construction of an actual camera the above means inevitably have an undesired influence on the effective picture plane.